Disease relapse is the most common reason for treatment failure of both autologous (auto) and allogeneic (alio) blood and marrow transplantation (BMT). As such, there is the unmet need to augment antitumor immunity in these settings. We propose a novel adoptive cell therapy (ACT) approach to augment antitumor immunity after autoBMT and to treat the post-transplant relapse after alloBMT by exploiting the unique characteristic of the bone marrow as both the primary anatomic site for most hematologic malignancies and a compartment enriched with tumor-reactive marrow infiltrating lymphocytes (MILs). We hypothesize that ex vivo activated tumor-specific MILs can impart measurable and sustainable antitumor immunity upon adoptive transfer. This hypothesis is formulated on the basis of our preliminary data and by bringing together innovative strategies developed during the previous funding cycle. MILs from multiple myeloma patients can be expanded ex vivo with anti-CD3/CD28 stimulation and activated as to significantly Increase their tumor specificity in ACT studies. Similarly, MILs obtained from patients undergoing alloBMT using PTCy-based GVHD prophylaxis can also be expanded, using the same techniques and augment their antitumor reactivity. Accordingly, in Specific Aim #1, we will determine if activated MILs in combination with an allogeneic myeloma cell vaccine or lenalidomide can augment and/or sustain antitumor immunity after autoBMT and assess the impact of activated MILs on immune reconstitution, tumor-specific immunity and correlate these parameters with clinical responses. In Specific Aim #2, we will conduct a phase l/ll clinical trial to evaluate the feasibility/safety of alloMILs obtained from the patient as a more tumor-specific